Though thunderstorms are familiar and seemingly non-threatening, severe thunderstorms can lead to dangerous supercells,derechos, and tornadoes.Severe thunderstorms are defined as having sustained winds above 93
kilometers (58 miles) per hour or unusually large hail, and there are
two key factors that fuel their formation: convective available potential energy
(CAPE) and strong wind shear. CAPE is a measure of how much raw energy
is available for storms; it relates to how warm, moist, and buoyant air
is in a given area. Wind shear is a measure of how the speed and direction of winds change with altitude.“CAPE can provide storms with the raw fuel to produce rain and hail,
and vertical wind shear can pull and twist weak storms into strong,
windy ones,” explained Harold Brooks, a meteorologist at NOAA’s National Severe Storms Laboratory.Scientists have evidence that global warming
should increase CAPE by warming the surface and putting more moisture
in the air through evaporation. On the other hand, disproportionate
warming in the Arctic should lead to less wind shear in mid-latitude
areas prone to severe thunderstorms. So one factor makes severe storms
more likely, while the other makes them less so.Researchers have developed detailed climate models (results shown
above) that aim to distinguish which of these opposing effects will
dominate as the climate changes. One study,
led by Robert Trapp of Purdue University, found that a doubling of
greenhouse gases in the atmosphere would significantly increase the
number of days that severe thunderstorms could occur in the southern and
eastern United States. Cities such as Atlanta and New York could see a
doubling of the number of days that severe thunderstorms could occur.The maps above show the results of a model comparing the summer
climate in 2072–2099 with the climate from 1962–1989. CAPE (top map) is
predicted to rise enough to overwhelm a slight decrease in vertical wind
shear (middle map), leading to an increase in severe thunderstorms
(third map), especially in Missouri and coastal North and South
Carolina. The modeling suggests that the increase in CAPE will be the
strongest in the Southeast and the decrease in wind shear strongest in
the Mountain West. The eastern United States will see more of an
increase in days favorable to severe thunderstorm formation than the
western part of the country.Read our feature In a Warming World, Storms May Be Fewer but Stronger to learn more about climate change and storms.